The transfer DNA (abbreviated T-DNA) is the transferred DNA of the tumor-inducing (Ti) plasmid of some species of bacteria such as Agrobacterium tumefaciens and Agrobacterium rhizogenes. It derives its name from the fact that the bacterium transfers this DNA fragment into the host plant's nuclear DNA genome. The T-DNA is bordered by 25-base-pair repeats on each end. Transfer is initiated at the left border and terminated at the right border and requires the vir genes of the Ti plasmid.
The bacterial T-DNA is about 20,000 base pairs long and contains genes that code for enzymes synthesizing opines and phytohormones. By transferring the T-DNA into the plant genome, the bacterium essentially reprograms the plant cells to grow into a tumor and produce a unique food source for the bacteria. The synthesis of the plant hormones auxin and cytokinin enables the plant cell to grow uncontrollably, thus forming the crown gall tumors typically induced by Agrobacterium infection. The opines are amino acid derivatives used by the bacterium as a source of carbon and energy.
Read more about Transfer DNA: T-DNA Transformation, Mechanism of T-DNA Transformation, T-DNA Mutagenesis
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